Electronic devices and systems have been employed for, among other applications, monitoring the pressure of tires mounted on a vehicle and providing the operator of the vehicle with information relating to tire pressure. These electronic devices and systems may also monitor other physical parameters of the tire, such as operating temperature. Many systems utilize radio frequency communication between the tire and an external interrogating device. A radio frequency communication link requires one or more antennas. Tire pressure may be monitored using an electronic device placed inside the air cavity of the tire. The electronic device may include a passive resonant circuit or may be capable of transmitting a radio frequency (RF) signal that reflects the monitored tire pressure to a remote receiver. The electronic device typically incorporates a unique identifying code carrying information for identification and tracking during manufacture, storage, distribution, and use.
The electronic device inside the tire includes one or more antennas used to transmit and receive the RF signals. The antenna may be helically shaped to absorb tensile and bending stress applied by to the tire during operation. The helical shape may also aid to prevent damage during manufacture of the tire. Most conventional antennas consist of a coiled wire formed of solid steel, copper or copper alloy, aluminum, or brass, or a steel core coated with either brass or zinc. In the latter constructions, the brass or zinc coating is applied to the steel wire during drawing and operates as a die lubricant. Consequently, the final thickness of zinc or brass on the spring steel is not intentionally controlled during manufacture of the antenna.
Although conventional antennas have been effective for their intended purpose, advances in antenna design are needed to optimize the properties of the electronic devices used in, for example, tires.